The report defines "inactive" as not achieving the government guidelines for physical activity of 150 minutes of moderate intensity physical activity a week and strength activities on at least two days a week.

Harriet had a busy life as an HR consultant, driving an hour to work and then sitting at a desk for eight to 10 hours a day.

She would then be busy with family life but didn't make time for activity or exercise.

"I just thought it was one of those things I'd get to in another point in time," she says.

The BHF analysis found that the average man in the UK spends a fifth of his lifetime sitting - equivalent to 78 days a year. For women, it is around 74 days a year.

Image copyrightBBC/BHF

Harriet had no symptoms or warning signs before her heart attack.

"I was climbing the stairs to go and brush my teeth and get ready for bed when I suddenly had the onset of severe chest pain which went down my left arm and into my upper jaw - it was at that point that I realised it was fairly serious.

'Crashing halt'

"We called an ambulance - which was exactly the right thing to do as the sooner you get help on a heart issue, the better your outcome is going to be."

Harriet had suffered from spontaneous coronary artery dissection (SCAD), a rare but dangerous condition which often strikes out of the blue and in people with few or no risk factors. It mainly affects young women.

"It was like having the rug pulled from under your feet," she says.

"You feel your life is going in a certain direction, you have a certain plan, you feel very confident about the way that your life is.

"I didn't have any long-term health conditions and then to suddenly be struck by such a traumatic incident was very difficult.

"It brought everything to a crashing halt for a short period of time while I collected myself and found myself again."

In the UK, physical inactivity contributes to almost one in 10 premature deaths from coronary heart disease, and one in six deaths from any cause.